Energy conversion systems are used to convert one form of energy to another form of energy. For example, an energy conversion system, such as an external combustion engine or external thermal engine, may convert heat energy into mechanical energy. To generate the heat energy, a combustion chamber may be used to combust various reactants (e.g., fuels and oxidizers) together in an exothermic reaction, such that the heat energy resulting from the reaction can be used to generate mechanical energy.